Download Classifying Types of Angles Expert Group

Polygons Expert Group
From the earliest recorded time, geometric shapes, such as triangles and rectangles, have
been used to decorate buildings and works of art. Triangles and rectangles are examples of
polygons. A polygon is a closed plane figure formed by three or more line segments. Each line
segment forms a side of the polygon, and meets, but does not cross, another line segment at a
common point. This common point is a vertex, or corner, of a polygon.
There are many types of polygons. Polygons are classified by the numbers of sides and
angles they have. A three-sided polygon is called a triangle. It also has three angles. A polygon with
four sides is a quadrilateral. A pentagon has five sides and a hexagon has 6 sides.
A seven-sided polygon is a heptagon. A polygon with 8 sides is an octagon and a polygon
with 9 sides is called a nonagon. A decagon has 10 sides. A regular polygon is a polygon in which
all sides are congruent and all angles are congruent. A stop sign is an example of a regular octagon.